Migration Patterns, Use of Stopover Areas, and Austral Summer Movements of Swainson's Hawks

Abstract

From 1995–1998, we tracked movements of adult Swainson’s Hawks (Buteo swainsoni) using satellite telemetry to characterize migration, important stopover areas, and austral summer movements. We tagged 46 hawks from July - September on their nesting grounds in seven U.S. states and two Canadian provinces. Swainson’s Hawks basically followed three routes south on a broad front, converged along the east coast of central Mexico, and followed a concentrated corridor to a communal austral summer area in central Argentina. North of 20° N, southward and northward tracks differed little for individuals from east of the Continental Divide but differed greatly (up to 1700 km) for individuals from west of the Continental Divide. Hawks left the breeding grounds mid-August to mid-October; departure dates did not differ by location, year, or sex. South migration lasted 42 to 98 days, and north migration took 51 to 82 days. On south migration, 36% of the Swainson’s Hawks departed the nesting grounds nearly 3 weeks earlier than the other radio marked hawks and made stopovers 9.0 – 26.0 days long in seven separate areas, mainly in the southern Great Plains, southern Arizona and New Mexico, and north-central Mexico. The austral period lasted 76 to 128 days. All Swainson’s Hawks used a core area in central Argentina within 23% of the 738800 km2 austral summer range where they frequently moved long distances (up to 1600 km). Conservation of Swainson’s Hawks must be an international effort that considers habitats used during nesting and non-nesting seasons including migration stopovers.

Autumn Raptor Migration in Yellowstone National Park, 2011–2015

“…Stopover areas are important for raptors to rest, forage and replenish fat reserves, and to complete molt (Kirby et al 2008;Kochert et al 2011;Pocewicz et al 2013;Craighead et al 2016;Vardanis et al 2016). Hayden Valley represents an undisturbed region within the Rocky Mountain Flyway in which raptors may recuperate after long flights.…”

“…Many raptors migrate across international and even continental boundaries (Kochert et al 2011). For example, Swainson's Hawks (Buteo swainsoni) have one of the longest migration routes of any raptor in the world (Fuller et al 1998;Bechard et al 2010;Kochert et al 2011).…”

“…Many raptors migrate across international and even continental boundaries (Kochert et al 2011). For example, Swainson's Hawks (Buteo swainsoni) have one of the longest migration routes of any raptor in the world (Fuller et al 1998;Bechard et al 2010;Kochert et al 2011). Each year tens of thousands of Swainson's Hawks leave their breeding grounds in westcentral North America for wintering areas in the open grasslands or pampas of Argentina in South America, a roundtrip of over 20 000 km (Bechard et al 2010;Kochert et al 2011).…”

“…For example, Swainson's Hawks (Buteo swainsoni) have one of the longest migration routes of any raptor in the world (Fuller et al 1998;Bechard et al 2010;Kochert et al 2011). Each year tens of thousands of Swainson's Hawks leave their breeding grounds in westcentral North America for wintering areas in the open grasslands or pampas of Argentina in South America, a roundtrip of over 20 000 km (Bechard et al 2010;Kochert et al 2011). Even short-distance migrants such as Golden Eagle (Aquila chrysaetos) and Rough-legged Hawk (Buteo lagopus) cross international boundaries from breeding areas in Alaska and Canada to wintering grounds throughout the western United States and Mexico (Bechard and Swem 2002;McIntyre et al 2008).…”

Space Use by Swainson’s Hawk (Buteo swainsoni) in the Natomas Basin, California

“…Isolated populations breed in interior valleys of British Columbia, Canada, California's Central Valley, and some valleys in the western Great Basin. The species winters from Mexico south through South America and occasionally in the southern United States [7,8]. Some individuals also winter in the Sacramento-San Joaquin Delta in California [9].…”